If you have an efficiency boost diverter and an engine focused distributor equipped, you can do constant boost spirals around them faster than their weapons can track you. It's also worth noting that their guns cant aim very high upward, so try to get into close range, then boost up above them to break their angle. If you run out of boost, you can use the safer window of time during a chaff to recharge your engines. Regardless of all this, you should still be able to win any head on fight with an eagle if you hit them consistently when they're popping heat sinks to lower your gimble radius and force you to aim, assuming you chaff and spin/strafe such that they don't hit you during your chaff, but you still hit them during their heat sinks. So either head on still and just practice aim a bit, or, if they have good enough aim to hit you even when you chaff, just spam boosts and spiral around whilst also doing your best to get above/behind their firing angle.